A known hydraulic power steering motor for a rack and pinion steering gear includes a housing. A rack bar extends through the housing. A piston is fixedly attached to the rack bar and divides the housing into first and second fluid chambers.
A fluid source provides fluid to the hydraulic power steering motor. The fluid source includes a reservoir, a fluid pump, a control valve, and a plurality of conduits. The pump pumps fluid from the reservoir to the control valve. A first conduit connects the pump and an inlet of the control valve. A second conduit connects an outlet of the control valve to the reservoir for returning fluid to the reservoir. Third and fourth conduits connect the control valve to the first and second chambers, respectively, of the power steering motor. If the control valve directs fluid toward the first chamber, the fluid pressure within the first chamber increases relative to the fluid pressure of the second chamber. If the control valve directs fluid toward the second chamber, the fluid pressure within the second chamber increases relative to the fluid pressure of the first chamber.
The fluid pressure in the first chamber and the fluid pressure in the second chamber act on the piston. When a sufficient differential pressure arises between the first and second chambers, the piston and the rack bar move relative to the housing for turning the steerable wheels of the vehicle.
The pump is typically a positive displacement pump. As a result, pulsations or pressure fluctuations arise in the fluid provided by the pump. Pulsations may also arise in response to manipulation of the control valve, such as during a steering maneuver. The pulsations may act on the piston of the power steering motor and may result in a driver perceptible noise or shudder in the power steering motor.